Have you downloaded the Android ADK software from Google? I believe that it contains libraries for accessing the host usb port. The MAX3421 is attached to the arduino via an I2C connection, so you will need to use that to communicate with it.

You have already been told this. The Max3421 is attached to the arduino via an I2C connection. You can use the Wire library to talk to it. The links ozracing gave you have sample code. You will need this https://dl-ssl.google.com/android/adk/adk_release_0512.zip. I don't have a Mega ADK. so I can't help any more than that.